HIV targets both lymphocytes and macrophages as host cells. Most studies equate progression to AIDS solely as the loss of T cell surveillance. However, it has been suggested that because HIV parasitizes macrophages, the virus could impair the microbicidal capacity of the phagocyte directly. Exploiting novel assays for phagosomal maturation we have demonstrated that HIV infection diminishes the hydrolytic capacity of the phagosome and impairs superoxide production. Given the macrophage's role as the primary barrier against microbial invasion this will have serious consequences, particularly at mucosal surfaces such as the respiratory tract. In this study we propose to address the following 3 questions. 1. To what extent does HIV infection compromise the anti-microbial capacity of macrophages? HIV-infected, PBMC-derived macrophages will be subjected to a panel of physiological assays to determine the extent to which phagocyte function is impaired i.e. phagosome acidification, the acquisition of lysosomal hydrolases, the generation of reactive oxygen and nitrogen intermediates, and the capacity of the HIV-infected cells to limit growth of a panel of model bacterial pathogens. 2. Do alveolar macrophages from HIV-infected patients demonstrate similar subversion of phagocyte function? Following in vitro validation, these assays will be repeated on broncholavage cells from HIV-infected patients at the Queen Elizabeth Hospital in Malawi. In addition, samples will be acquired for electron microscopy and for immuno-electron microscopy, and total nucleic acid will be extracted for retrospective identification of possible co-infections. 3. How does HIV impair macrophage function and can this be reversed chemotherapeutically? a. We propose functional studies to determine how HIV modulates the microbicidal capacity of the phagosome. b. We will conduct high-throughput screens to identify small molecules that counteract the suppressive activity of HIV. c. We will assay these compounds for their ability to reverse the suppression of phagocyte function in alveolar macrophages from HIV-infected patients.